The present invention relates to a heat radiation packaging structure for an exothermic electric part e.g. a relay etc. and a packaging method thereof.
Conventionally, degradation of soldered joints has been predominant in the case of mounting a large current electric part such as a relay onto a board using an ordinary eutectic solder, because of the large amount of heat generated by the electric part.
Therefore, a large current electric part has been mounted by soldering it on a electric wiring conductor coated with a resin mold, and by using a high melting point solder or by providing a heat radiation plate especially when an ordinary board may be used. As an exemplification, Japanese Patent Provisional Publication No. 11-40035/1999 discloses a connection structure for an electric part relating to a relay built-in controller. As shown in FIG. 1, a lead frame 1 comprising a metallic plate is used as a wiring conductor for a packaging board. In this prior technology, resin plates 2, 3 are disposed to sandwich the lead frame 1 therebetween.
Further, extruded portions 4 protruding downward almost cylindrically are disposed at the prescribed positions on the lead frame in order to pierce the resin plate 3. As shown in FIG. 2, a terminal 5A of a relay 5, for example, is inserted into the extruded portion 4 down from the upper surface of the resin plate 2, and is joined by filling a solder 6 in the extruded portion 4.
However, in the connection structure for an electric part according to said prior technology, since it is necessary to form the resin plates 2, 3 on the top and bottom surfaces respectively of the lead frame 1 in order to avoid adhering of resin onto the extruded portions, there has been the problems of making a manufacturing process complicated and resulting in a high cost of a product.
Further, since said prior technology includes the structure wherein the both sides of the lead frame 1 are covered with the resin plates 2, 3, there has been the problem of a decrease in a heat radiation ability.
Besides, when such a highly exothermic large current electric part is mounted on an ordinary printed wiring board, it becomes necessary to join them together with a high melting point solder or a high endurance solder and further to use an expensive printed wiring board comprising a board material with low thermal expansion.
Therefore, it has been necessary to make a board larger in dimension in order to maintain heat radiation using a wiring board consisting of the ordinary board material. Further, when such a packaging board is, for example, a board for a relay built-in on-vehicle controller, getting larger in size and area of the board itself may turn to be a cause which interferes getting an engine room smaller in volume.
Accordingly, the present invention aims to provide a heat radiation packaging structure for an electric part which does not cause getting a board itself larger in size, being excellent in heat radiation and low at cost, and to provide a method packaging of the electric part.
The 1st invention is a heat radiation packaging structure for an electric part, wherein a bus bar is fixed to a wiring board, joining a connecting terminal of an exothermic electric part onto the bus bar, sealing said wiring board, said bus bar, and said electric part with a heat conduction resin.
Therefore, since the heat generated from the exothermic electric part is directly conducted to the heat conduction resin in contact with the surface of the electric part and is then radiated outward, and is also conducted through the bus bar via a contact surface between the electric part and the bus bar, and is then radiated outward after conducting through the heat conduction resin in contact with the surface of the bus bar, an efficient heat radiation can be achieved. Moreover, since the heat conducted to the wiring board through the bus bar is also efficiently radiated from the heat radiating resin, the functions to restrain thermal degradation of the electric part and joint degradation of connected portion between the electric part and the bus bar can be provided.
Additionally, according to the 1st invention, it can be restrained for the wiring board to get larger because of an enhanced heat radiating ability using the heat conduction resin. Further, the functions to enhance humidity resistance and electrical insulation can also be provided by means of sealing the whole electric part with the heat conduction resin.
Besides, the 2nd invention is the heat radiation packaging structure for an electric part according to the 1st invention, wherein said bus bar includes a thermal diffusion portion which is bent up apart from said wiring board by means of a bent portion.
According to 2nd invention, since the thermal diffusion portion shaped by bending so as to be apart from the wiring board contacts the heat conduction resin on both the surfaces, an area of heat radiation can be increased and the ability in heat radiation can be enhanced.
Further, the 3rd invention is the heat radiation packaging structure for an electric part according to the 2nd invention as described above, wherein the bent portion of said bus bar contacts a side of said electric part. Therefore, according to 3rd invention, since the bent portion contacts the side of the electric part, the heat generated from the electric part can be well conducted toward the bus bar, restraining the electric part to increase greatly in temperature.
Besides, the 4th invention is the heat radiation packaging structure for an electric part according to any of the 1st-3rd invention as described above, wherein said heat conduction resin is contained in an outer case having a better heat radiation characteristic. According to the 4th invention, the heat stored in the heat conduction resin can be well radiated outward from the outer case.